I have just started a new thread, and after about 10 failures I have managed to submit it.
It appears that the post was simply too long, because it worked when I split the post into 4 parts, it worked correctly.
Wasn't there a warning some time ago when you wanted to post a big post ?
Also I noticed a new thing, the link manager stopped working after 28 links, I don't know if it's a problem of the browser or a problem of the "tool"